Synthetic grass sport surfaces are well known. They are used to replace natural grass surfaces which do not stand up well to wear and which require a great deal of maintenance. Also, natural grass surfaces do not grow well in partly or fully enclosed sport stadiums. The synthetic grass surfaces stand up to wear much better than the natural grass surfaces, do not require as much maintenance, and can be used in closed stadiums. Some synthetic grass surfaces comprise rows of strips or ribbons of a synthetic material, extending vertically from a backing mat with particulate material in-filled in between the ribbons on the mat. The ribbons of synthetic material usually extend a short distance above the layer of particulate material and represent blades of grass.
In order to reduce the abrasive nature of the synthetic grass infills and stabilize the top surface of the infills to retain a resilient grass-like surface that does not deteriorate in quality, or compact over time through use, a unique infilled layer of multiple distinct courses of a particulate material, for example, is disclosed in U.S. Pat. No. 5,958,527 which issued to Prevost on Sep. 28, 1999 and was assigned to the Assignee of this application. In Assignee's Canadian patent application No. 2,218,314, filed Oct. 16, 1997 and published on Sep. 10, 1998, the Assignee discloses a synthetic grass turf assembly.
When the synthetic grass turf assembly is installed on a sport field, however, an efficient drainage system under the grass turf assembly is needed because the water permeable backing cannot function well without a drainage system underneath to prevent water from accumulating on the turf surface. With certain infill materials, slow water evacuation could cause the infill material to float off of the surface, thereby creating an additional maintenance cost issue.
For example, U.S. Pat. No. 5,976,645, issued to Daluise et al on Nov. 2, 1999, discloses a vertical drainage system for a rubber-filled synthetic turf. The drainage system disclosed in this patent is deployed below a fabric backing layer of a synthetic turf and incorporates a porous geotextile membrane between an open graded aggregate layer and a sand layer above the aggregate layer to prevent the movement of one aggregate layer into the other. The drainage passages are generally formed with the 2-inch thick porous layer of sand and the 6-inch thick layer of sand and stone mixture. The draining rate depends on the particulate sizes and compact conditions of those layers. The porous geotextile membrane is used only for separating those two different layers.
A multiple-layer net structure for fluid drainage, particularly for geotechnical use, is well known in the art. A triplanar net, described in U.S. Pat. No. 5,255,998, which issued to Beretta on Oct. 26, 1993, for example, includes a first layer of mutually parallel wires which is rigidly associated with a second or intermediate layer of substantially mutually parallel wires, which are inclined with respect to the wires of the first layer. A third layer of wires is rigidly associated with the intermediate layer, on the opposite side thereof with respect to the first layer, and has substantially mutually parallel wires which are inclined with respect to the wires of the second or intermediate layer. In general and geotechnical use, such multiple-layer nets are buried and inclined with respect to the horizontal plane, so as to allow the drainage of any liquids to be eliminated from the region in which the drainage nets are located.
However, those multiple layer nets have not been suggested to be used in a drainage system for a synthetic grass turf assembly. Unlike other environments in which the multiple layer nets are used for drainage, a synthetic grass turf assembly for providing a game playing surface is a dynamic system continuously in movement under the influence of bouncing balls, vibration, and impacts from the feet and bodies of players in contact with the top surface of the turf. The more rigid grids do not alleviate the resilience of the synthetic turf. Many efforts have so far been made for improving such dynamic properties of synthetic grass turf assemblies.
Another problem with regard to the use of multiple layer nets in synthetic grass turf assembly is deformation resulting from radiant heat from the sun. A deformed multiple layer net not only statically affects the formation of a planar game playing surface but also jeopardizes the dynamic property thereof. For instance, the synthetic grass surface weight with an infill will not always correct the deformations caused by the curling of the edges of the net caused by absorbing heat from the sun. The net itself can form undulations by heat absorption both prior to and after the installation of the artificial grass system.
Therefore, there exists a need for a more efficient drainage system for a synthetic grass turf assembly, which meets the dynamic requirements for a game playing surface.